Most automotive vehicles are equipped with catalytic converters for purification of exhaust gas discharged from an internal combustion engine. The catalytic converters have been confirmed to have the following problems: When foreign matters such as welding spatter (produced during formation of exhaust manifold by pipe-welding or the like in a production process), remaining molding sand for casting, turnings produced in machining, and metal oxides produced during operation of the internal combustion engine reach a catalyst carrier in the catalytic converter, the foreign matters stay and move around on the upstream-side end face of the catalyst carrier without passing through the catalyst carrier. At this time, the foreign matters such as welding spatter move around on the upstream-side end face of the catalyst carrier, and therefore the upstream-side end face of the catalyst carrier will be changed in shape and damaged. Recently, such problems have become conspicuous owing to the fact that the honeycomb structure of the catalyst carrier has been reduced in wall thickness and increased in cell density in order to raise an exhaust gas purification efficiency, so that thereby the mechanical strength of the catalyst carrier is unavoidably lowered.
In view of the above problems, it has been proposed to trap the foreign matters such as welding spatter in order to prevent the foreign matters from moving around on the upstream-side end face of the catalyst carrier, as disclosed in Japanese Provisional Publication No. 2000-240440. This Publication discloses a carrier supporting mat for elastically supporting a monolithic catalyst carrier inside a casing. The carrier supporting mat in a flat state established before being wound around the catalyst carrier is formed at its end sections (to be jointed when the carrier supporting mat is wound) with inversed L-shaped portions and around its central section between the end sections with cuts which are generally parallel with the end sections. When the carrier supporting mat is wound around the catalyst carrier, the above inversed L-shaped portions are engaged with each other while the carrier supporting mat is brought into tight contact with the peripheral surface of the catalyst carrier upon a restoring force of the carrier supporting mat. Accordingly, long rectangular grooves and long V-shaped grooves are formed at the upstream-side end face of the carrier supporting mat in the wound state.